Conductivity is the measure of the
ease at which an electric charge or heat can pass through a material. A
conductor is a material which gives very little resistance to the flow of
an electric current or thermal energy. Materials are classified as metals,
semiconductors, and insulators. Metals are the most conductive and insulators
(ceramics, wood, plastics) the least conductive.

Electrical conductivity
tells us how well a material will allow electricity to travel through it.
Many people think of copper wires as something that has great electrical
conductivity.

Thermal conductivity
tells us the ease upon which thermal energy (heat for most purposes) can
move through a material. Some materials like metals allow heat to travel
through them quite quickly. Imagine that with one hand you are touching
a piece of metal and with the other, a piece of wood. Which material would
feel colder? If you said, "metal," you would be correct. But,
in fact, both materials are in fact the same temperature. This is relative
thermal conductivity. Metal has a higher heat transferability, or thermal
conductivity, than wood, letting the heat from your hand leave faster. If
you want to keep something cold the best idea is to wrap it in something
that does not have a high heat transferability, or high thermal conductivity,
this would be an insulator. Ceramics, and polymers are usually good insulators,
but you have to remember that polymers usually have a very low melting temperature.
That means if you are designing something that will get very hot the polymer
might melt, depending on its melting temperature.

Many products will contain both conductors
and insulators- the conductors take the electricity or thermal energy
where it is wanted and the insulators prevent it from getting where it
isn't wanted.

Silver has the highest electrical conductivity of all metals.
In fact, silver defines conductivity - all other metals are compared against
it. On a scale of 0 to 100, silver ranks 100, with copper at 97 and gold
at 76. Because of this property, and because it doesn't spark easily, silver
is commonly used in electrical circuits and contacts. Silver is also utilized
in batteries where dependability is mandatory and weight restrictions apply,
such as those for portable surgical tools, hearing aids, pacemakers and
space travel.